Sprinkler systems for watering lawns, schrubs, and other plants on sloping terrain are often arranged so that a main control valve for a number of water discharge heads is most conveniently positioned at an elevation that is above one or more of the discharge heads. A pipe system runs along and down the slope, interconnecting the control valve and discharge heads. In exceedingly steep terrain, or for plantings on the side of steep embankments, for example, a control valve at the top of the embankment may be many feet above a discharge head positioned near the foot of the slope. Accordingly, when the main control valve is shut off and water can no longer flow through the valve into the pipe system, the pipe system itself, at least for a short time, is still filled with water. Much of this pipe system, which connects the main control valve with all of the discharge heads, may be at an elevation considerably above that of some of the sprinkler heads. Accordingly, for a time immediately after the control valve shuts off the water supply, water in the pipe system continues to flow from the sprinkler heads. This water is under greatly decreased pressure and cannot be forcefully discharged to any useful distance from the sprinkler head, as is the case in normal operation of the discharge head with full water pressure from the open control valve. Because of the reduced pressure, water that drains from the pipe system to and through the discharge heads after shutoff of the control valve, collects at the foot of the risers supporting the respective discharge heads. This continued drain after main valve shutoff is undesired for a number of reasons: it is unsightly, it may collect in a pool of standing water (which itself can cause problems), and, in some cases, may continue to flow down portions of the slope with consequent tendencies toward errosion.
Accordingly, it is an object of the present invention to provide a sprinkler system that avoids or minimizes such problems.